Two studies were conducted to examine children-in-law's experiences of relational uncertainty and satisfaction during the transition to marriage. In Study 1, responses revealed children-in-law's (N = 154) myriad concerns revolving around three, broad themes of relational uncertainty: dyadic uncertainty, family system uncertainty, and individual uncertainty. Based on these results, we constructed scales of children-in-law's uncertainty for use in Study 2 (N = 204). Bivariate correlations revealed negative associations between children-in-law's uncertainty and relationship satisfaction within both the in-law and marital dyads. Collectively, these findings extend theoretical understanding of the role of relational uncertainty and social network influence during a crucial family transition.